Osteoarthrits (OA) is a pathology that is characterised by the erosion of the joint cartilage associated with the remodelling of the subchondral bone component with the formation of osteophytes.
The main causes of said pathology are the mechanical and biochemical changes affecting the joint as a whole.
These mechanical changes may be determined by irregularities in the joint system due to a number of possible causes, such as those listed below:                Slackening of the joint capsule;        Presence of loose bone matter within the joint;        Breakage of the menisci;        Joint trauma;        Erosions and/or incrustations of the joint capsule, ligaments and/or menisci, due to aging of the cartilage;        Inflammation of the joint system.        
Excessive and/or incorrect loading of the joint may trigger a chondrocyte response manifested by the synthesis of enzymes that are responsible for degradation of the cartilage.
The biochemical changes resulting from cartilage degradation translate into macrophage recruitment and, hence, inflammation involving the synovial membrane too, where an inflammatory reaction often leads to the synthesis of pro-inflammatory cytokines (such as IL-1), which spread through the synovial fluid, inciting the chondrocytes to produce pro-inflammatory cytokines too (such as IL-1, TNF, IL-6).
This super-expression of IL-1 is crucial to the pathogenesis of OA.
Indeed, IL-1 enhances the synthesis, secretion and activation of metalloproteins (MMP) by the chondrocytes, protein enzymes responsible for the degradation of the cartilage matrix, prevalently constituted by collagens and proteoglycans.
Moreover, said cytokine also proves to inhibit the proliferation of chondrocytes, suppress the production of the natural inhibitors of these metalloproteins (TIMPs), stimulate the synthesis of high levels of nitric oxide (NO) by the chondrocytes themselves, while inhibiting the synthesis of type-II collagen and aggrecan, a major component of the proteoglycans that constitute cartilage (Kafienah W. et al., Arthritis Rheum. 2003, 48:709-718).
The effect of IL-1 on joint cartilage has been amply documented by results obtained from in vivo experiments performed by infusing said interleukin into the joint, thus causing histological damage to the cartilage similar in all respects to that seen in OA (van Beuningen H. M. et al., Arthritis Rheum, 1991, 34:606-615).
All the experimental data on the OA process therefore strongly support the hypothesis that IL-1 (in particular IL-1 β), and probably TNFα too, represent the main catabolic system involved in the destruction of joint tissues and, moreover, that they may constitute an endogenous source of the molecules responsible for the aforesaid cartilage damage.
Indeed, it has been demonstrated that blocking the production and/or activation of IL-1 prevents and/or decreases destruction of the joint matrix (Caron J. P. et al., Arthritis Rheum, 1996, 39:1535-1544).
High levels of IL-1 have also been detected in the synovial fluid of patients suffering from rheumatoid arthritis (RA) and psoriatic arthritis (Arend W. P. et al., Arthritis Rheum, 1995, 38:151-160).
Hyaluronic acid (HA) is one of the main molecules constituting the cartilage matrix, but it also represents the chief non-protein component of the synovial fluid.
It is a strongly hydrophilic, viscoelastic molecule that imparts lubricating properties to the synovial fluid. For this reason, HA has been used to treat OA for over 30 years, and especially to treat the pain that accompanies the condition (Ghosh P. et al., Semin Arthritis Rheum, 2002, 32:10-37).
Various studies have provided data on the protective effect of HA in maintaining cartilage integrity during the pathological process of OA, by demonstrating how the polysaccharide lessens the disintegration of the joint tissue caused by IL-1 (Stove J. et al., Journal of Orthopaedic Research, 2002, 20:551-555).
For over a decade, the direct implantation of autologous chondrocytes into damaged cartilage tissue has been used as a technique for treating joint defects, even though new tissue engineering techniques are now becoming more commonplace, although they involve the application of tissues to cartilage that has mostly been damaged by trauma, so they are not applicable to degenerative pathologies such as OA (Freed L. E. et al., J Biomed Mater Res, 1993, 27: 11-23). U.S. Pat. No. 5,902,741 describes and claims a cartilage tissue prepared in vitro, comprising a three-dimensional matrix constituted by a biocompatible polymer (such as collagen, gelatine, PGA or synthetic polymers), in which stromal cells such as chondrocytes or fibroblasts can adhere and proliferate.
U.S. Pat. No. 5,736,372 describes and claims a three-dimensional structure for the preparation of cartilage to be subsequently implanted in vivo, constituted by a synthetic biodegradable polymer (optionally also in combination with a second, non-biodegradable polymer), wherein chondrocytes can be grown.
EP 0907721 describes and claims a substrate for the growth of cells (such as chondrocytes), formed by a sponge prevalently constituted by an HA derivative.
EP 1144459 describes and claims a composite, porous matrix composed of an HA derivative and gelatine, to be loaded with chondrocytes to form a tissue-engineered cartilage.
EP 1232203 describes and claims the preparation of a matrix constituted by chitosan to be implanted in vivo.
Numerous scientific studies have amply demonstrated that the hyaluronic acid esters are completely biocompatible, biodegradable polymer (Capoccia D. et al., Biomaterials, 1998, 19:2101-2127), that can induce and favour the adhesion, proliferation and re-differentiation of human joint chondrocytes previously expanded in vitro and then loaded onto a three-dimensional matrix formed by said derivative for the in vitro production of new cartilage containing, besides the cellular component, a new extracellular matrix (Brun P. et al., J Biomed Mater Res, 1999, 46:337-346; Aigner J. et al., J Biomed Mater Res, 1998, 42:172-181). WO 03/07873 describes and claims a porous matrix (sponge) formed mainly by plasma proteins (such as fibrin), for the adhesion and proliferation of stromal cells such as chondrocytes.
Also known is the use of HA derivatives in the form of fibres (European patent No. 0618817 B1) which, when made into a non-woven fabric, constitute a three-dimensional matrix (without a cell component) to be used in the field of dermatology; moreover, said three-dimensional structures may be loaded with mesenchymal cells and kept in vitro for as long as necessary for their proliferation and/or partial differentiation (European patent No. 0863776 B1), including differentiation into chondrocytes directed by specific trophic factors.
WO02/053201 discloses the use of a biological material containing cells supported on a three dimensional scaffold formed by a hyaluronic acid derivative and an other polymer selected from natural, synthetic or semisynthetic polymers for the preparation of grafts suitable for implantation by arthroscopic techniques.
To date, all the cartilage tissues obtained in vitro by tissue engineering techniques using biomaterials (constituted by natural, seminsynthetic or synthetic polymers) have proved to be useful only for implantation to correct cartilage lesions that are not connected with a degenerative and/or inflammatory pathology such as osteoarthritis.
Indeed, in an osteoarthritic lesion the main obstacle to implantation of a device such as those described above, lies in the high possibility/probability of inserting a tissue-engineered cartilage into a joint capsule that is rich in pro-inflammatory cytokines that would inevitably determine the onset of a slow degenerative pathology, rapidly affecting the new tissues too, with consequent slow degradation of the matrix molecules newly synthesised from the cartilage tissues introduced therein.
This hypothesis has already been verified in vitro using a scaffold constituted by PGA loaded with chondrocytes of bovine origin (Kafienah W. et al., Arthritis Rheum. 2003, 48:709-718).